Amount Of Quantum Entanglement Research Articles

Steady-state quantum correlation measurement in hybrid optomechanical systems

In this paper, we investigate the steady-state of quantum correlation measurement of hybrid optomechanical systems. The first system consists of a single optomechanical system simultaneously coupled to a mechanical oscillator. While the second system is a hybrid optomechanical system consisting of an atomic ensemble placed in between the optical cavity and mirror. For both optomechanical systems, we formulate the Hamiltonian and the explicit expression of the covariance matrix leading to the dynamic of the system. Under the linearization approximation, we investigate the steady-state quantum correlations which are quantified through the correlation function of non-Hermitian operators, while the logarithmic negativity is used to quantify the amount of quantum entanglement between the subsystems. Furthermore, our proposed quantum correlation function can be used to quantify the entangled bipartite states that are correlative and transfer information. It is found that the transfer of quantum correlations between the subsystem is related to the detuning and coupling strength. Our results provide a realistic route toward remote quantum entanglement detection and a framework of future realistic fiber-optic quantum network operating applications.

Investigation of Quantum Entanglement through a Trapped Three Level Ion Accompanied with Beyond Lamb-Dicke Regime

In this study, our goal is to obtain the entanglement dynamics of trapped three-level ion interaction two laser beams in beyond Lamb-Dicke parameters. Three values of LDP, η=0.09, η=0.2 and η=0.3 are given. We used the concurrence and the negativity to measure the amount of quantum entanglement created in the system. The interacting trapped ion led to the formation of phonons as a result of the coupling. In two quantum systems (ion-phonons), analytical formulas describing both these measurements are constructed. These formulas and probability coefficients include first order terms of final state vector. We report that long survival time of entanglement can be provided with two quantum measures. Negativity and concurrence maximum values are obtained N = 0.553 and for LDP = 0.3. As a similar, the other two values of LDP are determined and taken into account throughout this paper. For a more detailed understanding of entanglement measurement results, “contour plot” was preferred in Mathematica 8.

Quantum entanglement in de Sitter space from stringy axion: An analysis using α vacua

In this work, we study the phenomena of quantum entanglement by computing de Sitter entanglement entropy from von Neumann measure. For this purpose we consider a bipartite quantum field theoretic set up for axion field, previously derived from Type II B string theory compactified to four dimensions. We consider the initial vacuum to be CPT invariant non-adiabatic α vacua state under SO(1,4) isometry, which is characterised by a real one-parameter family. To implement this technique we use a S2 which divide the de Sitter into two exterior and interior sub-regions. First, we derive the wave function of axion in an open chart for α vacua by applying Bogoliubov transformation on the solution for Bunch-Davies vacuum state. Further, we quantify the density matrix by tracing over the contribution from the exterior region. Using this result we derive entanglement entropy, Rényi entropy and explain the long-range quantum effects in primordial cosmological correlations. Our results for α vacua provides the necessary condition for generating non zero entanglement entropy in primordial cosmology.

Statistical Aspects and Dynamical Entanglement for a Two-Level Atom Moving on Along Cavity Length of x-Direction: Atomic Position Distribution

In this work, the problem of the quantum optical model is considered where an one-mode quantized radiation field interacts with a two-level atom (TLA). Also, the atomic position distribution is taken into account, i.e., the atom passing through the length of the optical cavity. We believe that the atomic position affects the matter-field interaction and can be realized in several multiple experiments, such as ultracold atoms and trapped ions. We take into consideration the atom is moving along the cavity field in the x-direction so that the time-position Schrodinger equation for the atom in the x-direction is obtained. We suppose that the field is initially prepared in a coherent state optical field and the atom is initially prepared in an excited state. Also, the atomic motion along the cavity length vanishes in the cavity wall. By using the Laplace transformation method, an exact analytical solution for the coupled partial differential Schrodinger equation for the wave function is calculated. Some non-classical statistical aspects such as the atomic inversion and the photon distributions are discussed in detail. The collapses-revivals, the Poissonian distributions of the photon by Mandel Q parameter, the degrees of the entanglement, and the fidelity have been investigated. The effect of the atomic position distribution in the x-direction on these phenomena is examined. We observed that the atomic position distribution along the cavity has an effective effect on the quantum statistical properties of these phenomena. Minutely, the influence of the atom location distribution on the amount of quantum entanglement has been obtained.

Pure state entanglement harvesting in quantum field theory

Quantum fields in vacuum states carry an infinite amount of quantum entanglement, and its entanglement entropy has the ultraviolet divergence. Harvesting protocols of the vacuum entanglement had been investigated, but its efficiency is very low to date. The main reason of the low efficiency originates from the fact that the extracted entanglement is embedded in a mixed state of two external devices. We propose a general protocol with high efficiency by extracting pure state entanglement from the field. We only use bi-linear interactions between the fields and external devices. Even though the ultraviolet cutoff remains finite, the protocol is capable of extracting a huge amount of entanglement. Hence the infinite amount of entanglement extraction is attained without the ultraviolet divergence of the field entanglement entropy in a continuum limit. There exists a trade-off relation between the extracted entanglement and its energy cost.

Production, Entanglement and Polarization of Nonlinear Excited Entangled Coherent States of Some Realizations of the SU(1,1) and SU(2) Groups

In this paper, at first we produce the single-mode nonlinear excited entangled SU(1,1) and SU(2) coherent states via the iterated actions of the f-deformed creation operator A ‡ = f(n)a ‡ on the first mode of a particular class of entangled states which components correspond to respectively SU(1,1) and SU(2) coherent states. In the continuation, we study the amount of quantum entanglement and quantum polarization of the produced states for different number of photon excitations m and compare the results. We show that similar behaviours for entanglement properties are appeared for the introduced entangled SU(1,1) and SU(2) states. Also, the existence of a parameter by which one can obtain the maximum possible values of linear entropy for lower intensities is established. It is established that the increasing rate of concurrence (as well as the linear entropy) and so entanglement grows up by increasing the number of photon excitation. Meanwhile, the polarization variation is different for the SU(1,1) and SU(2) coherent states for the fixed excitation numbers. Finally, we present a simple scheme for the physical generation of the introduced states.

Higher dimensional entangled qudits in a trapped three-level ion

Quantum entangled states in a system of trapped three-level ion interacting with two laser beams in Λ (Lambda) configuration is investigated. We have characterized a typical family of initial conditions for their potential to generate quantum entanglement of internal and external degrees of freedom of the ion. It is found that entangled qudits, specifially qutrits and quadrits, can be optimally for a certain preparation of the ionic system. Analytical results, describing the quantum entangled state explicity, are presented. The amount of quantum entanglement is quantified directly by calculating the generalized concurrence for arbitrary qudits. It is obtained that higher dimensional entanglement can be established with the Lamb-Dicke parameter (LDP). The LDP dependence of Schmidt coefficients is shown.